1. Field of the Invention
The present invention relates to photolithographic deposition of CRT screens, including formation of black matrices and phosphor deposits. The present invention relates more specifically to photostencils used in near contact to the photosensitized faceplate to provide for interchangeable mask and screen type cathode ray tubes (CRTs).
2. Discussion of the Related Art
Those familiar with the art of phosphor screen application to the faceplate of a display device, such as the common color cathode ray tube, are aware of the advantages to be gained by utilizing near contact photoexposure techniques. Such advantages are set forth in the parent application, U.S. Ser. No. 07/655,561, filed Feb. 13, 1991, now U.S. Pat. No. 5,158,491. The parent application is herein incorporated by reference to avoid lengthy exposition of background unnecessary to the exposition of the present invention for those ordinarily skilled in the art.
Briefly, however, the near contact photoexposure screening technique, hereinafter called "near contact printing," utilizes a standardized photostencil placed very close to the photosensitive coating on the CRT faceplate to be exposed. The result is that each faceplate screened by near contact printing is alike in feature size and location to a high degree. This enables likewise standardized shadow masks to be fitted interchangeably in operable relation to the standardized screens.
As set forth in the parent application, an ideal photostencil, called the "parent stencil", for use in near contact printing is made, preferably by photoplotting. The pattern of photostencil features is dictated by the electron-optic characteristics of the operable CRT which govern the paths of the electron beams used to excite the phosphor deposits on the screen. This method of parent stencil generation is time consuming and expensive. The parent photostencil, or duplicates thereof, used in the screen exposure apparatus have a fixed photo-stencil pattern, the discrete elements, or light-passing apertures, of which will be referred to as the aforementioned "features."
Thus, the parent stencil is fixed in an idealized feature pattern but has only one feature size and shape. However, the requirements of the screen features in a given model of tube may change from time to time, due, perhaps, to changing tube specifications or to take advantage of other manufacturing efficiencies or cost saving. Thus, to introduce flexibility of feature size and/or shape to the CRT screen without generating a new parent stencil is highly desirable.
Since the parent stencil cannot be economically used in a factory environment, due to its high cost and susceptibility to damage, it is necessary to form progeny stencils, i.e., working copies therefrom. Because there is no need to duplicate electron beam optics with the near contact exposure apparatus, the parent stencil can be made in any manner necessary to create a working progeny stencil of proper pattern for exposure of the CRT screen. The present invention therefore, teaches the formation of a parent stencil proportional and featured so as to allow near contact print generation of the working progeny thereby enabling changes in the feature size and shape while retaining the feature pattern dictated by electron beam landings in the CRT. Control of the generation of progeny to maintain feature acuity is, of course, central to the present invention.